The present invention relates to a novel excipient for use in the manufacture of pharmaceuticals, and in particular, solid dosage forms such as tablets which include one or more active ingredients.
In order to prepare a solid dosage form containing one or more active ingredients (such as drugs) it is necessary that the material to be compressed into the dosage form possess certain physical characteristics which lend themselves to processing in such a manner. Among other things, the material to be compressed must be free-flowing, must be lubricated, and, importantly, must possess sufficient cohesiveness to insure that the solid dosage form remains intact after compression.
In the case of tablets, the tablet is formed by pressure being applied to the material to be tabletted on a tablet press. A tablet press includes a lower punch which fits into a die from the bottom and a upper punch having a corresponding shape and dimension which enters the die cavity from the top after the tabletting material fills the die cavity. The tablet is formed by pressure applied on the lower and upper punches. The ability of the material to flow freely into the die is important in order to insure that there is a uniform filling of the die and a continuous movement of the material from the source of the material, e.g. a feeder hopper. The lubricity of the material is crucial in the preparation of the solid dosage forms since the compressed material must be readily ejected from the punch faces.
Since most drugs have none or only some of these properties, methods of tablet formulation have been developed in order to impart these desirable characteristics to the material(s) which is to be compressed into a solid dosage form. Typically, the material to be compressed into a solid dosage form Includes one or more excipients which impart the free-flowing, lubrication, and cohesive properties to the drug(s) which is being formulated into a dosage form.
Lubricants are typically added to avoid the material(s) being tabletted from sticking to the punches. Commonly used lubricants include magnesium stearate and calcium stearate. Such lubricants are commonly included in the final tabletted product in amounts of less than 1% by weight.
In addition to lubricants, solid dosage forms often contain diluents. Diluents are frequently added in order to increase the bulk weight of the material to be tabletted in order to make the tablet a practical size for compression. This is often necessary where the dose of the drug is relatively small.
Another commonly used class of excipients in solid dosage forms are binders. Binders are agents which impart cohesive qualities to the powdered material(s). Commonly used binders include starch, and sugars such as sucrose, glucose, dextrose, and lactose.
Disintegrants are often included in order to ensure that the ultimately prepared compressed solid dosage form has an acceptable disintegration rate in an environment of use (such as the gastrointestinal tract). Typical disintegrants include starch derivatives and salts of carboxymethylcellulose.
There are three general methods of preparation of the materials to be included in the solid dosage form prior to compression: (1) dry granulation; (2) direct compression; and (3) wet granulation.
Dry granulation procedures may be utilized where one of the constituents, either the drug or the diluent, has sufficient cohesive properties to be tabletted. The method includes mixing the ingredients, slugging the ingredients, dry screening, lubricating and finally compressing the ingredients.
In direct compression, the powdered material(s) to be included in the solid dosage form is compressed directly without modifying the physical nature of the material itself.
The wet granulation procedure includes mixing the powders to be incorporated into the dosage form in, e.g., a twin shell blender or double-cone blender and thereafter adding solutions of a binding agent to the mixed powders to obtain a granulation. Thereafter, the damp mass is screened, e.g., in a 6- or 8-mesh screen and then dried, e.g., via tray drying, the use of a fluid-bed dryer, spray-dryer, radio-frequency dryer, microwave, vacuum, or infra-red dryer.
The use of direct compression is limited to those situations where the drug or active ingredient has a requisite crystalline structure and physical characteristics required for formation of a pharmaceutically acceptable tablet. On the other hand, it is well known in the art to include one or more excipients which make the direct compression method applicable to drugs or active ingredients which do not possess the requisite physical properties. For solid dosage forms wherein the drug itself is to be administered in a relatively high dose (e.g., the drug itself comprises a substantial portion of the total tablet weight), it is necessary that the drug(s) itself have sufficient physical characteristics (e.g., cohesiveness) for the ingredients to be directly compressed.
Typically, however, excipients are added to the formulation which impart good flow and compression characteristics to the material as a whole which is to be compressed. Such properties are typically imparted to these excipients via a pre-processing step such as wet granulation, slugging, spray drying, spheronization, or crystallization. Useful direct compression excipients include processed forms of cellulose, sugars, and dicalcium phosphate dihydrate, among others.
A processed cellulose, microcrystalline cellulose, has been utilized extensively in the pharmaceutical industry as a direct compression vehicle for solid dosage forms. Micro-crystalline cellulose is commercially available under the tradename EMCOCEL(copyright)(copyright) from Edward Mendell Co., Inc. and as Avicel(copyright) from FMC Corp. Compared to other directly compressible excipients, microcrystalline cellulose is generally considered to exhibit superior compressibility and disintegration properties.
Another limitation of direct compression as a method of tablet manufacture is the size of the tablet. If the amount of active ingredient is high, a pharmaceutical formulator may choose to wet granulate the active with other excipients to attain an acceptably sized tablet with the desired compact strength. Usually the amount of filler/binder or excipients needed in wet granulation is less than that required for direct compression since the process of wet granulation contributes to some extent toward the desired physical properties of a tablet. Thus, despite the advantages of direct compression (such as reduced processing times and costs), wet granulation is widely used in the industry in the preparation of solid dosage forms. Many of those skilled in the art prefer wet granulation as compared to direct compression because this method has a greater probability of overcoming any problems associated with the physical characteristics of the various ingredients in the formulation, thereby providing a material which has the requisite flow and cohesive characteristics necessary to obtain an acceptable solid dosage form.
The popularity of the wet granulation process as compared to the direct compression process is based on at least three advantages. First, wet granulation provides the material to be compressed with better wetting properties, particularly in the case of hydrophobic drug substances. The addition of a hydrophilic excipient makes the surface of a hydrophobic drug more hydrophilic, easing disintegration and dissolution. Second, the content uniformity of the solid dosage forms is generally improved. Via the wet granulation method, all of the granules thereby obtained should contain approximately the same amount of drug. Thus, segregation of the different ingredients of the material to be compressed (due to different physical characteristics such as density) is avoided. Segregation is a potential problem with the direct compression method. Finally, the particle size and shape of the particles comprising the granulate to be compressed are optimized via the wet granulation process. This is due to the fact that when a dry solid is wet granulated, the binder xe2x80x9cgluesxe2x80x9d particles together, so that they agglomerate in the granules which are more or less spherical.
Due to the popularity of microcrystalline cellulose, pharmaceutical formulators have deemed it desirable to include this excipient in a formulation which is wet granulated prior to tabletting. Unfortunately, currently-available microcrystalline cellulose does not hold to the typical principle that the amount of filler/binder needed in wet granulation is less than that in direct compression. It is known that the exposure of the microcrystalline cellulose to moisture in the wet granulation process severely reduces the compressibility of this excipient. The loss of compressibility of microcrystalline cellulose is particularly problematic where the formulation dictates that the final product will be relatively large in the environment of use. For example, if a pharmaceutical formulator desires to prepare a solid oral dosage form of a high dose drug, and the use of the wet granulation technique is deemed necessary, the loss of compressibility of the microcrystalline cellulose dictates that a larger amount of this material may be needed to obtain an acceptably compressed final product. The additional amount of microcrystalline cellulose needed adds cost to the preparation, but more importantly adds bulk, making the product more difficult to swallow.
The loss of compressibility of microcrystalline cellulose when exposed to wet granulation has long been considered a problem in the art for which there has been no satisfactory solution.
Attempts have been made to provide an excipient having high compressibility, a small bulk (high apparent density), and good flowability, while being capable of providing satisfactory factory disintegration of the solid dosage form, which is applicable to wet granulation as well as to dry granulation and direct compression methods for preparation of solid dosage forms.
For example, U.S. Pat. No. 4,159,345 (Takeo, et al.) describes an excipient which consists essentially of a microcrystalline cellulose having an average degree of polymerization of 60 to 375 and obtained through acid hydrolysis or alkaline, oxidative degradation of a cellulosic substance selected from linters, pulps and regenerated fibers. The microcrystalline cellulose is said to be a white cellulosic powder having an apparent specific volume of 1.6-3.1 cc/g, a repose angle of 35xc2x0 to 42xc2x0, a 200-mesh sieve residue of 2 to 80% by weight and a tapping apparent specific volume of at least 1.4 cc/g.
In U.S. Pat. No. 4,744,987 (Mehra, et al.), a particulate co-processed microcrystalline cellulose and calcium carbonate composition is described wherein the respective components are present in a weight ratio of 75:25 to 35:65. The co-processed composition is said to be prepared by forming a well-dispersed aqueous slurry of microcrystalline cellulose and calcium carbonate and then drying the slurry to yield a particulate product. The combination of these two ingredients is said to provide a lower cost excipient which has tabletting characteristics similar to those of microcrystalline cellulose and which would satisfy a need for an economical excipient with good performance that is desired by the vitamin market.
European Patent Application EP 0609976A1 (assigned to Asahi Kasei Kabushiki Kaisha) describes an excipient comprising white powdery microcrystalline cellulose having an average degree of polymerization of from 100 to 375, preferably from 190 to 210, and an acetic acid holding capacity of 280% or more, preferably from 290 to 370%. The excipient is said to exhibit high compactability and a high rate of disintegration and is said to be obtained by heat-treating an aqueous dispersion of purified cellulose particles, which has a solids content of 40% or less by weight, at 100xc2x0 C. or more, followed by drying, or by subjecting an aqueous dispersion of purified cellulose particles having a solids content of 23% or less by weight to thin film-forming treatment and drying the resultant thin film. The excipient is said to possess a high compressibility, and a good balance of compactability and rate of disintegration.
There still remains a need in the industry for a pharmaceutical excipient which possesses excellent compressibility whether utilized in a direct compression or wet granulation procedure.
It is an object of the present invention to provide an excipient which is useful in a variety of applications, and which may be utilized in direct compression or wet granulation methods.
It is a further object of the present invention to provide an excipient useful in direct compression methods which has improved compressibility relative to microcrystalline cellulose.
It is a further object of the present invention to provide an excipient useful in wet granulation methods which has improved compressibility relative to microcrystalline cellulose.
It is a further object of the present invention to provide a free-flowing excipient which has excellent compressibility properties when utilized in direct compression or wet granulation methods, and which furthermore possesses pharmaceutically acceptable disintegration properties.
It is a further object of the present invention to provide an improved microcrystalline cellulose excipient in which the microcrystalline cellulose has not been chemically altered, and which has improved compressibility relative to xe2x80x9coff-the-shelfxe2x80x9d commercially available microcrystalline cellulose.
It is a further object of the present invention to provide a solid dosage form which includes one or more active ingredients and the improved microcrystalline cellulose excipient of the present invention.
It is a further object of the present invention to provide an oral solid dosage form for one or more drugs which is economical to manufacture, which maintains its integrity during storage, and which possesses excellent disintegration and dissolution properties when exposed, e.g., to gastrointestinal fluid.
In accordance with the above objects and others which will be obvious to those skilled in the art, the present invention is directed to an excipient comprising a particulate agglomerate of coprocessed microcrystalline cellulose and from about 0.1% to about 20% silicon dioxide, by weight of the microcrystalline cellulose, the microcrystalline cellulose and silicon dioxide being in intimate association with each other, and the silicon dioxide portion of the agglomerate being derived from a silicon dioxide having a particle size from about 1 nanometer (nm) to about 100 microns (xcexcm), based on average primary particle size.
In preferred embodiments, the silicon dioxide comprises from about 0.5% to about 10% of the excipient, and most preferably from about 1.25% to about 5% by weight relative to the microcrystalline cellulose.
In additional preferred embodiments of the invention, the silicon dioxide has a particle size from about 5 nm to about 40 xcexcm, and most preferably from about 5 nm to about 50 xcexcm.
In preferred embodiments of the present invention, the silicon dioxide is further characterized by a surface area from about 10 m2g to about 500 m2/g, preferably from about 50 m2/g to about 500 m2/g, and more preferably from about 175 m2/g to about 350 m2/g.
The present invention is further directed to an aqueous slurry useful in the preparation of a compressible excipient useful in dry and wet granulation formulation methods, comprising a mixture of microcrystalline cellulose and from about 0.1% to about 20% silicon dioxide, by weight relative to the microcrystalline cellulose, the silicon dioxide having a particle size from about 1 nm to about 100 xcexcm. The solids content of the aqueous slurry is from about 0.5% to about 25%, by weight, preferably from about 15% to about 20% by weight, and most preferably from about 17% to about 19% by weight.
The present invention is further directed to a mixture of an active ingredient(s) and an excipient comprising a particulate agglomerate of coprocessed microcrystalline cellulose and from about 0.1% to about 20% silicon dioxide, by weight of the microcrystalline cellulose, the microcrystalline cellulose and silicon dioxide being in intimate association with each other, and the silicon dioxide having a particle size from about 1 nm to about 100 xcexcm. The ratio of active ingredient to excipient is from about 1:99 to about 99:1, by weight.
The present invention is further directed to a granulate of an active ingredient(s) and the novel excipient described herein, wherein the active ingredient(s) and excipient have been subjected to a wet granulation procedure.
The present invention is further directed to a compressed solid dosage form comprising an active ingredient(s) and the novel excipient described herein, wherein the active ingredient(s) and excipient have been directly compressed into the solid dosage form or have been subjected to a wet granulation procedure and thereafter compressed into the solid dosage form. The compressed solid dosage form provides a suitable immediate release dissolution profile of the active ingredient(s) when exposed to aqueous solutions during in-vitro dissolution testing, and provides a release of drug in an environment of use which is considered bioavailable. In further embodiments of the invention, the dissolution profile of the solid dosage form is modified to provide a controlled or sustained release dissolution profile.
The present invention is further directed to a method of maintaining and/or enhancing the compressibility of microcrystalline cellulose. The method includes forming an aqueous slurry containing a mixture of microcrystalline cellulose and silicon dioxide having a particle size from about 1 nm to about 100 xcexcm, and drying the slurry to obtain microcrystalline cellulose-based excipient particles in which the silicon dioxide particles have been integrated with the microcrystalline cellulose particles. Within this aspect of the invention, the slurry contains from about 0.5% to about 25% by weight microcrystalline cellulose, with amounts of from about 15% to about 20% being preferred. Furthermore, the slurry contains from about 0.25% to about 5% by weight silicon dioxide.
The novel excipient described herein is free-flowing, possesses excellent disintegration properties, and importantly, in certain embodiments possesses improved compressibility relative to normal xe2x80x9coff-the-shelfxe2x80x9d commercially available microcrystalline cellulose when directly compressed. The advantages of the novel excipient described herein are especially realized in pharmaceutical formulations prepared using wet granulation techniques. When utilized in wet granulation techniques, the novel excipient surprisingly provides a compressibility which is substantially improved in preferred embodiments in comparison to the compressibility of normal xe2x80x9coff-the-shelfxe2x80x9d commercially available microcrystalline cellulose used in wet granulation and is even comparable to xe2x80x9coff-the-shelfxe2x80x9d microcrystalline cellulose used in direct compression techniques. In other embodiments, the novel excipient surprisingly provides a compressibility which is substantially superior to the compressibility of normal xe2x80x9coff-the-shelfxe2x80x9d commercially available microcrystalline cellulose used in direct compression techniques.
The term xe2x80x9cenvironmental fluidxe2x80x9d is meant for purposes of the invention to encompass, e.g., an aqueous solution, or gastrointestinal fluid.
By xe2x80x9csustained releasexe2x80x9d it is meant for purposes of the invention that the therapeutically active medicament is released from the formulation at a controlled rate such that therapeutically beneficial blood levels (but below toxic levels) of the medicament are maintained over an extended period of time, e.g., providing a 12 hour or a 24 hour dosage form.
By xe2x80x9cbioavailablexe2x80x9d it is meant for purposes of the invention that the therapeutically active medicament is absorbed from the sustained release formulation and becomes available in the body at the intended site of drug action.
By xe2x80x9cprimary particle sizexe2x80x9d it is meant for purposes of the invention that the particles are not agglomerated. Agglomeration is common with respect to silicon dioxide particles, resulting in a comparatively average large agglomerated particle size.